The invention relates to an adjustment device for a friction clutch, which is provided in order to compensate an extension of the engagement paths, for example in case of reducing thickness of the friction coatings of the friction clutch. Such adjustment devices and/or friction clutches are particularly useful in clutches of motor vehicles during start-up.
In a friction clutch a plurality of friction areas are made to contact in order to transfer a torque, while a relative motion occurs between these friction areas. Here, mandatorily wear and tear occurs in the form of material abrasion such that the distance between the two friction areas increases by the reduction of the thickness of the friction coatings over the course of the increasing wear and tear of the friction clutch. Adjusting units must generate considerable forces, requiring expensive construction. Here, in spite of a change of the thickness of the friction coatings over the duration of use, it is advantageous for the engagement units to particularly describe a constant and short engagement path. In order to avoid the displacement path of the engagement unit becoming unnecessarily long, recently many applications started to use adjustment devices. The wear and tear of the friction coatings is dependent on the shifting behavior as well as the use of the friction clutch and thus here the adjustment of the extending engagement path must be set individually for the respective abrasion of each friction clutch. Additionally, settling behavior develops in friction clutches, which can be compensated by an adjustment device.
In order to change the distance between the friction areas it has become common to use a ramp construction at the rear of the pressure plate with a corresponding ramp construction at a displacement ring. By rotating the displacement ring in the circumferential direction the position of the pressure plate is changed axially in the friction clutch, leading to the distance between the friction areas to be altered. The engagement device, impacting the rear of the displacement ring, describes here an almost constant engagement path. In order to rotate the displacement ring devices are used in prior art which are aligned tangentially in reference to the circumference of the pressure plates, for example a worm drive, a spindle, or a sprocket. In such constructions it is disadvantageous that particularly worm drives and spindle drives are subject to high centrifugal forces, which are directed perpendicular to their axial alignment. Therefore, the bearings of such adjustment devices must be embodied in a particularly robust fashion, and the play between the elements of the adjustment device must be kept low. This renders such adjustment devices to be also particularly sensitive to temperature changes.